Cathodic Protection

Cathodic protection is one option for protecting an underground storage tank (UST) from
corrosion. There are two types of systems for cathodic protection:

Sacrificial anode

Impressed current

Sacrificial anodes can be attached to a
coated1 steel UST for corrosion
protection (see below, left and center).
Sacrificial anodes are pieces of metal more electrically active
than the steel UST. Because these anodes are more active, the
corrosive current will exit from them rather than the UST. Thus,
the UST is protected while the attached anode is sacrificed.
Depleted anodes must be replaced for continued corrosion protection
of the UST.

An impressed current system uses a rectifier to
convert alternating current to direct current (see below, right). This current is sent
through an insulated wire to the anodes, which are special metal
bars buried in the soil near the UST. The current then flows
through the soil to the UST system and returns to the rectifier
through an insulated wire attached to the UST. The UST system is
protected because the current going to the UST system overcomes the
corrosion-causing current normally flowing away from it.

Federal regulations require that the cathodic protection systems
installed at UST sites (field-installed) be designed by a corrosion expert.

The
system must be tested by a qualified cathodic protection tester
within six months of installation and at least every three years
thereafter. In addition, cathodic protection systems must be tested within six months of any repair to any cathodically protected UST system. You will need to keep the results of the last two tests
to prove that the cathodic protection is working. In addition, you
must inspect an impressed current system every 60 days to verify
that the system is operating. Keep results of your last three
60-day inspections to prove that the impressed current system is
on and operating properly.

This is an illustration of cathodic protection by using sacrificial anodes.

This is an illustration of cathodic protection by using sacrificial anodes.

This is a line diagram of cathodic protection by impressed current.

1 The coating must be of a suitable
dielectric material (i.e., a coating that electrically isolates
the UST from its environment and meets applicable industry codes).
An asphaltic coating is not considered a suitable dielectric
coating.